conio.h required for getch??

the getch() function is defined in conio.h.
However the getch() works perfectly without including conio.h in the program.
the same thing is also applicable to some other functions such sqrt(),malloc() etc.
are these functions defined in stdio.h also or is there something else i don't know.

The function is only defined in the headers file mentioned under the help but sometimes when you include one header file it internally include some other files and so you can use them but it depends on the compiler you are using and when you use some other compiler then it will not work as expected.